Robotic CNC Table

The table was probably made in the 90s. It has a total of 18 inch movement in X and Y directions. The lead screws have a .25inch pitch. The motors that came with the table were too old to be used, and some new servos were retrofitted.

The servos also came from on ebay.

Their specs are the following:

    37.51 Oz-In/A
    25.0-30.5 V/KRpm
    Motor Terminal Resistance .75-1.02 Ohms @ 4A. 
    Maximum Terminal Voltage 60V
    Maximum Continuous Speed 2100 RPM (No Load)
    Maximum Peak Torque 1500 Oz-In.
    Maximum Peak Current 44.5A
    Maximum Continuous Stall Torque At Max Motor Temp 300 Oz-In. 
    Maximum Continuous Current 8.9A

US digital motor encoders were used to detect the position of the motor relative to turns of the lead screw.

The new motors were so large that they dont fit the nema 34 sized system on my table.

At Stock Drive Products, they have piles of cad drawings, pdf files specifying pulleys and belts, and a straight-forward ordering system. I had to make an educated guess about the length of the belts, so using the data from the sdp site I put the geometry of the motors, pulleys and ballscrews in autocad and figured out the number of teeth required for the correct length belt.

After getting the anticipated position of the motor the motor mounts were designed and plans were sent off to a machinist:

...who made the parts out 3/8th inch aluminum plate.

The CNC table also needed to have a rack added that would support parts that are getting cut by the laser. The rack has to be level, because the distance from the laser that can develop the power density to cut metal can only vary by a less than a millimeter. The table itself is machined aluminum, very flat, and served as a good platform for the rack. The rack was made of 3/4 inch aluminum bar stock. Its held together with threaded rod. Aluminum tubes were cut 1 3/4 inch for spacers.

There are neodymium ring magnets attached with small bolts in on each bar.

The neodymium rings came from ebay. If you search on neodymium you'll get a million hits. Nice stuff, but you cant machine it, so the ring variety was purchased for easy bolting.

Next generation table

The only other construction item was the brackets that were placed in the assembly to bolt the blade-unit to my cnc table. The brackets were cut by my table and folded into the a C-shape. Its nice to have a system that can help build itself.

This is a picture of the blades holding up a piece of stainless steel. The t-shaped brackets laying flat on the table have bolts that project down and wing nuts bring up a part below the table to hold down the steel.

In my previous set up, when the laser passed over the part getting cut in the areas where the bars contacted the part, it would splash in funny ways producing problematic cuts. In the new system the point of contact to the part is relatively small, when the laser passes over where the supporting table there's no splashing. The tips of the points on the blades are machined well enough they form a nice flat surface. Once assembled together with the threaded rod they are very ridged and dont flex in left to right or up and down directions. The blades came from ebay and cost about $100 total.